# Stepwise

Stepwise regresion modeling explained in detail.

**Stepwise Regression Modeling**

Stepwise regression is used for automatic feature selection in regression modeling. It is a variable selection method that sequentially adds or removes variables from a regression model based on certain criteria, such as statistical significance, to arrive at an optimal model.

There are two main types of stepwise regression: forward stepwise regression and backward stepwise regression.

**Forward Stepwise Regression**

In forward stepwise regression, the model starts with no predictors and iteratively adds one predictor at a time to the model based on a predetermined criterion, such as the highest increase in adjusted R-squared or the lowest p-value. The process continues until no further improvement is observed according to the chosen criterion.

**Backward Stepwise Regression**

In backward stepwise regression, the model starts with all predictors included and iteratively removes one predictor at a time from the model based on a predetermined criterion, such as the lowest decrease in adjusted R-squared or the highest p-value. The process continues until no further improvement is observed according to the chosen criterion.

Stepwise regression can also include a combination of forward and backward steps, known as bidirectional stepwise regression, where variables can be added or removed from the model based on the chosen criterion.

Stepwise regression can be useful in situations where there are a large number of potential predictor variables and the goal is to identify the most important variables for the regression model. It automates the process of variable selection and helps to identify a subset of predictors that are most relevant for the model based on the chosen criterion.

Stepwise regression has some limitations. It can be computationally intensive, as it involves fitting multiple models with different subsets of predictors. It may also result in overfitting, as the selected subset of predictors may not generalize well to new data. Careful validation and evaluation of the final model obtained through stepwise regression are essential to ensure its validity and reliability.

Stepwise regression is used for automatic feature selection and model building, and its results should be interpreted with caution, taking into consideration the potential limitations and assumptions of the method.